Recovery of chlorine from hydrogen chloride produced in carbochlorination process

Abstract

The invention relates to a method for recovering chlorine from hydrogen chloride generated in a carbon chlorination process. Furthermore, the invention relates to the use of the method for recovering chlorine from hydrogen chloride produced in a carbochlorination process.

Description

Technical Field

[0001] The present invention relates to a method for recovering chlorine from hydrogen chloride produced in a carbochlorination process. In addition, the present invention relates to the use of the method for recovering chlorine from hydrogen chloride produced in a carbochlorination process. Background Art

[0002] The carbochlorination process is a process in which metal oxides are converted to their corresponding metal chlorides in the presence of chlorine and a carbonaceous material. The most common carbochlorination process involves the processing of feedstocks such as ores and slags containing oxides of refractory metals (among which are niobium, tantalum, tungsten, molybdenum and rhenium) or oxides of rare earth metals such as cerium, neodymium, samarium or oxides of light metals such as aluminium, silicon, vanadium or titanium or other metals such as zirconium or other metal oxides. The metal chlorides generally exhibit a low vapour pressure and can be removed from the original solid matrix by sublimation or can be purified by fractional sublimation or distillation, taking advantage of their varying boiling points, with or without the use of solvents. In addition, the metal chlorides can also be purified by extraction or other separation methods.

[0003] Typically, the metal chlorides are further processed into metals, metal alloys, or purified oxides or hydroxides, all of which are economically attractive.Carbochlorination processes and the challenges associated with the use of chlorine in these processes will be further discussed in more detail using exemplary titanium dioxide.

[0004] Titanium dioxide is manufactured by the widely accepted sulfate process or the chloride process. The latter uses a titanium-containing raw material that is subjected to a carbochlorination process. The chloride thus obtained is subsequently separated by resublimation or distillation. The titanium tetrachloride is finally converted into titanium dioxide, and the chlorine released from the above reaction is separated and reused in the reaction with the titanium-containing raw material. Among other reasons, the reuse of chlorine makes the chloride process economically more attractive than the sulfate process.

[0005] In the case of titanium-containing feedstocks containing significant amounts of components other than titanium, particularly iron, reusing the chlorine reacted with the titanium-containing feedstock is very burdensome. Since chlorides other than titanium tetrachloride are separated and removed from the process, the chlorine from these components cannot be easily recovered and the internal recycle is therefore lost, making the process economically unattractive.

[0006] In order to compensate for the loss of chlorine, new chlorine must be added to the system, which is associated with increased costs. The higher the content of components other than titanium, the higher the compensation for the loss. Therefore, it is generally preferred to have a high titanium dioxide content of at least 90wt.% and a low content of other elements (especially iron) raw materials, which can be converted into their chlorides and produce by-products with relatively low commercial value. Titanium-containing slag and natural rutile meet these beneficial criteria. Disadvantageously, the production of titanium-containing slag requires high energy input, and global natural rutile resources are increasingly limited. Due to the attractiveness of the chloride process, the demand for natural rutile is also increasing. The increasing demand leads to higher prices for these rutiles. In addition, the available amount of titanium sources (such as ilmenite) is higher, but contains a large amount of iron, which will make the cost of the chloride process significantly higher due to the above reasons.

[0007] Patent application EP21172411.7 also faces the above challenges by using titanium-containing raw materials containing iron. The raw material is contacted with chlorine in a carbon chlorination reactor, and the metal contained in the raw material is reacted with chlorine. After separating the ferrous chloride obtained in this way from titanium tetrachloride, sulfuric acid is reacted with ferrous chloride to obtain hydrogen chloride and ferric sulfate via anion exchange. Then, for example, hydrogen chloride is converted into chlorine by the Deacon process, and it can be reintroduced into the carbon chlorination reactor. However, ferric sulfate is contaminated by heavy metals and other impurities (for example, coke, ore residues, etc. from the carbon chlorination reactor). The contaminated monohydrate has a lower commercial value and needs to be processed or purified, which of course brings undesirable additional costs.

[0008] In summary, the use of the carbochlorination process to separate metals from ores or slags, depending on the composition of the slag or ore used as raw material, results in significant losses of chlorine due to the presence of other metals, especially iron, in the slag or ore used. This makes the overall carbochlorination process costly, less sustainable and therefore less attractive.

[0009] Therefore, there is a need in the art for a method of recovering chlorine from hydrogen chloride in a carbochlorination process using a metalliferous feedstock having iron which is economically attractive with significantly lower by-products of low commercial value. Summary of the invention

[0010] The object of the present invention is to provide an improved process for recovering chlorine from hydrogen chloride in a carbochlorination process which is economically attractive and has significantly lower by-products of low commercial value.

[0011] This object is achieved by the method and use according to the invention.

[0012] The invention provides a method for recovering chlorine from the hydrogen chloride produced in a carbochlorination process, wherein the metal-containing raw material comprises iron. The metal chloride obtained can be separated and further processed into a desired final product, such as respective metals, metal alloys or purified oxides or hydroxides. The method advantageously allows chlorine to be recovered from ferric chloride, i.e. ferrous chloride and / or ferric chloride, by separating ferric chloride and then subjecting the ferric chloride to a hydrolysis step to obtain iron oxide and hydrogen chloride. The latter is subsequently converted into chlorine by using the Deacon process and can be reused in the carbochlorination process. Therefore, natural ores with high metal content and expensive artificial slag are not the only qualified sources as raw materials in the carbochlorination process, which makes the method and use according to the present invention economically beneficial.

[0013] Therefore, in a first aspect, the present invention relates to a method for recovering chlorine from hydrogen chloride produced in a carbochlorination process, the method comprising the following steps: a) contacting a carbonaceous material and chlorine with a metalliferous raw material to obtain a chloride mixture, the metalliferous raw material comprising iron, the chloride mixture comprising ferrous chloride and / or ferric chloride and metal chloride, b) separating ferrous chloride and / or ferric chloride from the chloride mixture, c) subjecting the ferrous chloride and / or ferric chloride to a hydrolysis step to obtain hydrogen chloride, d) converting at least a portion of the hydrogen chloride obtained into chlorine, and, optionally, e) using at least a portion of the chlorine obtained in step a) in step d).

[0014] As a second aspect, the present invention relates to the use of the method disclosed herein for recovering chlorine from hydrogen chloride produced in a carbochlorination process.

[0015] Further advantageous embodiments of the invention are stated in the dependent claims. DETAILED DESCRIPTION

[0016] These and other aspects, features and advantages of the present invention will become apparent to those skilled in the art by studying the following detailed description and claims. Each feature of one aspect of the present invention may be used in any other aspect of the present invention. Numerical ranges stated in the format "from x to y" include the values ​​mentioned and within the corresponding measurement accuracy known to those skilled in the art. If several preferred numerical ranges are stated in this format, all ranges formed by the combination of the various endpoints are of course also included.

[0017] In step a) of the process according to the invention, a carbonaceous material and chlorine are contacted with a metal-containing raw material containing iron to obtain a chloride mixture containing ferrous chloride and / or ferric chloride and a metal chloride. Preferably, the metal-containing raw material contains up to 70 wt.%, preferably up to 60 wt.%, more preferably up to 50 wt.% of iron, based on the total weight of the metal-containing raw material. With regard to the feature "metal-containing raw material containing iron", it is meant that the metal is any metal other than iron. The metal is preferably selected from refractory metals, rare earth metals and light metals. More preferably, the metal is selected from niobium, tantalum, tungsten, molybdenum, rhenium, zirconium, cerium, neodymium, samarium, aluminum, silicon, vanadium or titanium, even more preferably titanium. The metal may be present in the raw material as its corresponding element, as a salt and / or as an oxide, typically as its corresponding oxide. The iron of the metal-containing raw material may also be present in oxidation state (II) or (III) as its corresponding element, as a salt and / or as an oxide, typically as the corresponding oxide. Any carbonaceous material may be used, which contains enough carbon to produce the sufficient reduction potential and temperature required for the carbochlorination process. The material may be selected from petroleum coke, carbon produced by pyrohydrolysis, charcoal produced from different sources (e.g. wood, seeds, etc.), carbon black and soot. Additional metals and metalloids may be present in the raw material. As a result of step a), a chloride mixture comprising ferrous chloride and / or ferric chloride and metal chlorides is obtained.

[0018] From the chloride mixture consisting of metal chloride and ferrous chloride and / or ferric chloride obtained in step a), ferrous chloride and / or ferric chloride are separated from the chloride mixture in a subsequent step b). This can be achieved by common techniques such as resublimation or distillation, but can also be achieved by extraction or any other separation method. Preferably, the ferrous chloride and / or ferric chloride are purified before step c) to remove impurities, including unreacted metal-containing raw materials and unreacted carbonaceous materials adhering to the above-mentioned chlorides.

[0019] In step c), ferrous chloride and / or ferric chloride are subjected to a hydrolysis step to obtain hydrogen chloride. Ferrous chloride and / or ferric chloride are obtained in step b). Preferably, step c) is carried out at a high temperature of 120°C to 350°C, preferably 160°C to 260°C, more preferably 180°C to 240°C in the presence of a modifier. The modifier is a medium for hydrolysis. It can be composed of an inert or reactive salt melt, an ionic liquid, a deep eutectic solvent, a non-aqueous solvent, whether or not a co-solvent is added. In one embodiment of the present invention, a salt melt composed of zinc chloride has been found to be particularly advantageous for the hydrolysis reaction, and if ferrous chloride is the main substance in the metal chloride phase, the hydrolysis reaction can be carried out in a slurry, or if ferric chloride is the main substance in the metal chloride phase, the hydrolysis reaction can be carried out in a homogeneous melt. Alternatively, if ferric chloride is present during step c), the hydrolysis reaction can be further carried out without a modifier. A specific initial amount of water can be added to the selected modifier to increase their viscosity, which is beneficial to the operation of the process. During the hydrolysis reaction, the amount of water in the regulator is kept constant at an initial level, wherein the level is selected so that the vapor pressure of the water above the mixture is always lower than the vapor pressure of the hydrogen chloride. This enables gaseous hydrogen chloride to be recovered from the hydrolysis reaction virtually free of water.

[0020] As used herein, "anhydrous" hydrogen chloride means that the water concentration in the gaseous hydrogen chloride does not exceed 15 vol.%, and can be as low as within the range of 0.01 vol.% of the total weight of hydrogen chloride and water. When ferrous iron is the main ferric chloride species, the hydrolysis reaction can be supported by the introduction of oxygen or other oxidants. Typically, iron oxide in the form of hematite is obtained as a by-product.

[0021] In another preferred embodiment of the present invention, the hydrolysis in step c) is carried out as a pyrohydrolysis at a temperature of 600° C. to 1200° C., preferably 700° C. to 1000° C., more preferably 800° C. to 900° C. For this purpose, a spray roasting device as used in the so-called Ruthner process can be used, in which natural gas is oxidized in the presence of oxygen in a reactor. Alternatively, the Lurgi process can be carried out in a fluidized bed for pyrohydrolysis.

[0022] In a preferred embodiment, the water produced in the hydrolysis or pyrohydrolysis process is removed to the level required for gas phase oxidation of hydrogen chloride over the Deacon catalyst. Therefore, in a preferred embodiment of the present invention, water is removed from hydrogen chloride before step d) so that the hydrogen chloride contains at most 25 vol.%, preferably at most 15 vol.%, more preferably at most 5 vol.%, even more preferably at most 1 vol.% of water based on the total volume of gaseous hydrogen chloride and gaseous water. This is achieved by common techniques and equipment for obtaining gaseous hydrogen chloride.

[0023] Then, in step d), at least a portion of the hydrogen chloride obtained is converted into chlorine. Hydrogen chloride is obtained in step c). In a preferred embodiment of the invention, the conversion is carried out at an elevated temperature, generally in the range of 400°C to 450°C in the presence of a catalyst, although specific catalysts may allow this temperature range to be significantly reduced. For example, application EP0980340.5 discloses a catalyst, preferably a supported ruthenium oxide catalyst, which allows the lower temperature of the temperature range to be reduced to 100°C. It is known to those skilled in the art that the oxidation of hydrogen chloride is an equilibrium reaction. If the reaction is carried out at high temperatures, the equilibrium conversion rate decreases. Therefore, the oxidation is preferably carried out at low temperatures of 100°C to 300°C. The catalysts and methods disclosed in EP0980340.5 are incorporated herein by reference. Catalysts that can also be used in this step are based on copper chloride, i.e., known mixtures of copper (I) chloride and copper (II) chloride, zinc chloride or based on iron chloride.

[0024] Other catalysts include ruthenium oxide, cerium oxide or chromium (III) oxide supported on tin oxide, silicon dioxide, titanium dioxide, aluminum oxide or lanthanum oxide. The oxidation of hydrochloric acid to chlorine based on a catalyst is also known as the so-called Deacon process. A process using a so-called fixed bed reaction system, in which hydrogen chloride and oxygen are passed through a catalyst bed, which is formed by filling reaction tubes with a catalyst for producing chlorine. In the case of industrial-scale oxidation of hydrogen chloride by a fixed bed reaction system, a fixed bed multitubular reactor is usually used. In this oxidation reaction, a large amount of catalyst for producing chlorine is required to form a catalyst bed in all these reaction tubes.

[0025] In another preferred embodiment, the hydrogen chloride generated in step c) is subjected to an absorption step in water, an aqueous hydrochloric acid solution having a concentration of 28 wt% to 34 wt% of hydrogen chloride is generated before the conversion in step d), and the conversion is carried out by electrolysis. When the water content in the gaseous hydrogen chloride before the absorption exceeds 25 vol.% of the total weight of water and gaseous hydrogen chloride, electrolysis using an oxygen depolarized cathode (ODC) is particularly suitable. Both conversion techniques are well known in the art.

[0026] The chlorine obtained can be used as a valuable raw material in the production of vinyl chloride or phosgene. Optionally, in step e), at least a portion of the chlorine obtained can be used in step a) and thus recycled. Before the chlorine is reused in step a), water is removed from the chlorine to the level required for carbon chlorination.

[0027] The method steps herein are performed in the following order: a), b), c), d), and then e).

[0028] In the case where the metal of the metal-containing feedstock is titanium, the feedstock is preferably selected from ilmenite, perovskite, rutile, titanite or mixtures thereof. Techniques and equipment commonly used in the chloride process, such as a reactor for performing the carbochlorination reaction, wherein a fluidized bed may be employed in this step.

[0029] In another aspect of the invention, the method disclosed herein is used to recover chlorine from hydrogen chloride produced in a carbochlorination process. Preferably, the carbochlorination process is used in a chloride process to obtain titanium dioxide. The latter is particularly suitable as a white pigment in lacquers, paints and decorative paper applications.

Claims

1. A method for recovering chlorine from hydrogen chloride produced in a carbochlorination process, the method comprising the following steps: a) contacting a carbonaceous material and chlorine with a metalliferous source material, the metalliferous source material comprising iron, to obtain a chloride mixture comprising ferrous chloride and / or ferric chloride and a metal chloride, b) separating ferrous chloride and / or ferric chloride from the chloride mixture, c) subjecting the ferrous chloride and / or ferric chloride to a hydrolysis step to obtain hydrogen chloride, d) converting at least part of the hydrogen chloride obtained into chlorine, and, optionally e) using in step a) at least a portion of the chlorine obtained in step d).

2. The method according to claim 1, characterized in that Step c) is carried out at a temperature of 120 to 350°C, preferably 160 to 260°C, more preferably 180 to 240°C in the presence of a regulator.

3. The method according to claim 1, characterized in that The hydrolysis in step c) is carried out as a pyrohydrolysis at a temperature of 600 to 1200°C, preferably 700 to 1000°C, more preferably 800 to 900°C.

4. The method according to any one of claims 1 to 3, characterized in that The hydrogen chloride obtained in step c) comprises water and the water is removed from the hydrogen chloride before step d) such that the hydrogen chloride contains at most 25% by volume, preferably at most 15% by volume, more preferably at most 5% by volume, even more preferably at most 1% by volume of water, based on the total volume of gaseous hydrogen chloride and gaseous water.

5. The method according to any one of claims 1 to 4, characterized in that The metal is selected from refractory metals, rare earth metals and light metals, preferably titanium.

6. The method according to any one of claims 1 to 5, characterized in that The metal of the metalliferous feedstock is titanium and the feedstock comprises at most 70 wt%, preferably at most 60 wt%, more preferably at most 50 wt% iron, based on the total weight of the titanium-containing feedstock.

7. The method according to claim 6, characterized in that The titanium-containing raw material is selected from ilmenite, perovskite, rutile, sphene or a mixture thereof.

8. The method according to any one of claims 1 to 7, characterized in that Step d) is carried out at elevated temperature in the presence of a catalyst and oxygen.

9. The method according to claim 8, characterized in that The catalyst is selected from ruthenium oxide, cerium oxide, chromium (III) oxide, cupric chloride, ferric chloride and zinc chloride.

10. The method according to claim 9, characterized in that The catalyst is supported on tin oxide, silicon dioxide, titanium dioxide, aluminum oxide, lanthanum oxide or a mixture thereof.

11. The method according to any one of claims 1 to 7, characterized in that Said hydrogen chloride produced in step c) is subjected to an absorption step in water before the conversion in step d), and the conversion of at least part of the hydrogen chloride obtained into chlorine is carried out by means of electrolysis.

12. Use of the method according to any one of claims 1 to 10 for recovering chlorine from hydrogen chloride produced in a carbochlorination process.

13. Use of the method according to claim 11, characterized in that The carbochlorination process is used in the chloride process to obtain titanium dioxide.